The present invention relates to valves in general, and more particularly to improvements in valves which are, or which can be, equipped with means for influencing the fluid flowing therethrough. The expression "influencing" means is intended to embrace a filter, a device which determines a particular characteristic (such as the temperature, pressure, rate of flow and/or others) of the conveyed fluid, a device which removes samples of conveyed fluid, or a combination of such devices. Still more particularly, the invention relates to improvements in valves wherein the valving element is disposed between first and second passages which are defined by the valve housing or body and respectively serve for admission of a fluid (particularly a hydraulic fluid) into and for evacuation of the fluid from the housing. Such valves are often used in hydraulic pipe lines to allow for monitoring of the characteristics of conveyed fluid, to allow for admission of controlled quantities of one or more additives, to allow for filtering or otherwise cleaning of the conveyed fluid and/or to allow for removal of samples at regular or irregular intervals.
A drawback of presently known valves which are equipped with removable or interchangeable fluid-influencing inserts or components is that the fluid is likely to spill when the housing is opened to allow for insertion of a fresh component or for removal of a previously inserted component. Attempts to prevent uncontrolled outflow of fluid include the provision of a shutoff valve at the inlet side of the valve housing, the provision of discrete shutoff valves at the inlet and outlet sides of the housing, or the provision of a shutoff valve at the inlet side and a check or non-return valve at the outlet side of the housing. This contributes significantly to the overall cost of the valve and, moreover, a check valve cannot always ensure adequate sealing of the outlet side against leakage of fluid on removal of a portion of the housing so as to gain access to the fluid-influencing component.
It was further proposed to provide a valve which contains a removable fluid-influencing component with a switchover device which is designed to allow the incoming hydraulic fluid to flow from the inlet toward the outlet and through a filter or an analogous component, or directly from the inlet to the outlet (i.e., so that the fluid bypasses the filter). The switchover device is actuatable by a spring which is installed in the path of the conveyed fluid. Such mode of preventing leakage on opening of the housing is also unreliable because the spring is dependent upon the flow conditions, i.e., such switchover devices also cannot reliably ensure that no fluid will escape when the operator wishes to gain access to a previously inserted fluid-influencing component or to provide room for insertion of a fresh component. The problem is aggravated when the conveyed fluid is a corrosive, explosive or otherwise hard-to-handle substance which should be kept out of contact with the hands of the operators, with the surrounding atmosphere, and/or with unprotected portions of the valve. Moreover, and especially if the valve includes a switchover device and the fluid-influencing component is a filter, the fluid which flows through the housing of the valve while the switchover device is activated (i.e., while an attendant exposes the space for reception of a filter) does not undergo any filtering or analogous cleansing action. This might adversely influence the parts which receive fluid from a pipe line or another fluid conveying system wherein the valve is installed.